Role of neurogenic factors in canine urethral wall tension and urinary continence.

A plastic disc, secured submucosally, was inserted in the canine bladder to permit filling of the bladder neck region while bypassing the accommodating ability of the detrusor. The bladder neck region was distended with radiopaque solution and the onset of flow in the urethra and the width of the urethra at steady state flow conditions were monitored by fluoroscopy. Perfusion pressure was also recorded. Bilateral section of the hypogastric nerves produced a substantial reduction in the time to initial flow and an increase in the width of the urethra with a decrease in pressure at steady state flow. Bilateral section of the pelvic nerves or administration of atropine reduced urethral wall tension at steady state flow but did not significantly influence the onset of initial flow. Gallamine treatment had no significant effect either on wall tension or on the onset of initial flow. It was estimated that the sympathetic nervous system contributed about 30 per cent to the urethral wall tension at steady state flow conditions whereas the parasympathetic nervous system contributed about 10 per cent. The remaining 60 per cent was attributed to the elastic properties of the urethra. In the maintenance of urinary continence, the sympathetic nervous system was estimated to contribute almost 60 per cent based on our experimental system. No other neurogenic influence was found to contribute significantly. Elastic and mechanical (anatomic) factors were probably responsible for the remaining 40 per cent. It was concluded that the sympathetic nervous system has a significant role in the maintenance of urinary continence.